Abstract: A reasonable and authentic estimate of surface rupture shortening amount of reverse fault is essential to a thorough understanding of the co-seismic surface deformation parameters,while we have no effective or feasible methods to deal with it,presently.The paper attempts to analyze and calculate horizontal shortening amounts of reverse fault with trench excavation basing on the investigations of the surface ruptures of the M_S 8.0 Wenchuan earthquake.On this condition,we conclude three genesis models of fault scarp,namely,faulting,flexuring,and superposition of faulting and flexuring.The paper proposes several calculation methods about horizontal shortening amounts of reverse fault based on these fault scarp models,and also gives detailed mathematic proof and constraint factors when considering complicated phenomena.Moreover,combined with these models,we discuss how to correctly apply and interpret the reverse surface rupture information revealed by trench.Finally,we demonstrate the calculation process and results of the reverse fault's horizontal shortening amounts in the trench close to the Central School of Bailu and the trench at Quanxin village of Hanwang,which are(2.83?0.3)m and(0.61?0.11)m,respectively.

Key words: M_S 8.0 Wenchuan earthquake, reverse fault, horizontal shortening amount, trench

摘要： 合理估计逆断层地表破裂缩短量是全面认识同震地表变形参数的核心内容,目前还没有较成熟的方法。以汶川M_S 8.0地震地表破裂为例,尝试通过探槽开挖来研究逆断层水平缩短量的计算问题。在分析汶川地震同震变形的基础上,总结了3种陡坎的成因模式:断层断错地表型、挠曲型、断层与挠曲叠加型,并依据这些模型提出了一些水平缩短量的计算方法及其限制条件,以及如何理解逆断层地表破裂探槽开挖所揭示的信息。最后给出了汶川M_S 8.0地震白鹿中心学校和汉旺全新村两地点水平缩短量的求解过程及结论,计算得到白鹿中心学校探槽水平缩短量为(2.83±0.3)m,汉旺全新村探槽水平缩短量为(0.61±0.11)m。

关键词: 汶川M_S 8.0地震, 逆断层, 水平缩短量, 探槽